Cick on the record in FamilySearch, Right click on the image , open in new window. There will be a download button on the right just above the image. Click download. At the bottom left is two tabs Image Index and Information, Click on Information, This contains you reference. Scroll a little down with you mouse wheel and there is a tab Copy Citation. Click on that.
Now open the profile where the record belongs. On the top is a row of tabs. Click on Images. Click on "Click here to upload it"
The new page that opens you can right click and paste the source citation you copied on FamilySearch. Just above it you click to browse for the file you downloaded.
Complete any other boxes that are there and at the bottom choose Source instead of Photo